What to do before try-outs?

conditioning-

definitely practice jumping rope once a day... you can do fifty normal, fifty sideways,etc.. max jumps are also really good! you jump as high as you can during each jump. double jumps( not sure what these are called actually), where you swing the rope twice in one jump.

i think another person mentioned this one- if you have stairs or a sturdy box practice stepping up or jumping up onto the box or stair, and switch legs after you do 25 or so.

LOTS OF PUSHUPS!!! these tremendously help you core muscles!!! wall pushups, wide pushups(where you put your hands really far apart), fast pushups (where you do them really quickly in a row), and also do pushups where you touch your nose to the ground between reps..

practice lifting weights!!! five pound ones work well. do arm circles forwards and backwards

dead man setting- i dont know if you are a setter, but these are still good! you start laying down with a ball in your hands. then you slowly rise up while setting until you have reached standing position. also crunch setting where you do a crunch while setting.

i am adding this part because i didnt finish my answer above..

as for practicing your skills-

i am assuming since you are trying out for a national team, you are already pretty good.. but depending on your position you are trying out as you should really practice according to that. if you play ds or libero practice with someone throwing a ball really far and then getting under it or practice defense while your sister hits.. i dont really have advice for if you are a setter besides the conditioning part bcuz i am not a setter.. if you play middle practice hitting, blocking, and swiping (i think you said you have a volleyball net in your backyard).. if you are outside,opp, or right side practice hitting.. also if you are trying out for the top national team, the coaches will definitely be looking for strong servers!! practice, practice, practice your serve!! practice your jump float or topspin, your short serve, your floater, topspin, and deep serve.. also practice serving to specific positions as this will be a jey thing that the coaches will look for. say a position in your head and practice serving to that position with your volleyball net.

hope this helps and good luck!!

Jumping Higher-

Set out some boxes or crates or something you can safely jump onto and not break, and do your approach and jump on to them. Make the stack higher and higher as you go along.

Improve aim with serves-

YOu know that game around the world? where you serve to someone and they have to catch it and then you go around the court in every position? Well you can do this with your sister, yr both on opposite teams, and use boxes or crates as targets, you have to get the ball to go inside the box/crate.

Conditioning-

Try to condition once or twice a week for 45 minutes-

Try to condition your abs most of all (they help you hit harder) use a medicine ball or if you dont have one fill up a old ball full of dirt or rocks and duct tape the cut you made shut

Do specific drills for your position.

Go to a gym and work out

Do Athletic Republic if there is one near you

I don't have many, but one good idea that I have is to do that "half squat" position that you do in volleyball. Try doing whenever. Not many people can hold that position for very long if they're doing it right. :)